The present invention relates to a method and system for controlling fuel for an engine, and more particularly, to a method and system for controlling fuel for an engine that prevents a lean Air/Fuel ratio from occurring at the beginning of sudden acceleration.
A fuel system for a vehicle generally includes a system for reclaiming evaporated gas. This system gathers the evaporated gas, which is generated according to flow and temperature of fuel in the fuel tank, and bums it by routing it into the intake system of the engine. The gathered evaporated gas flows into the intake system through a solenoid controlled purge control valve that is operated according to the driving state of the vehicle. This prevents evaporated gas from polluting the air.
But evaporated gas includes both air and fuel components, making it difficult to maintain a desired theoretical Air/Fuel ratio by only controlling the amount of fuel injected. Also, driving conditions and the resulting engine load (e.g., engine RPM, and the negative pressure state in the intake manifold, which varies according to engine load) change the amount of evaporated gas passing through the purge control valve at any one time.
Additionally, it is difficult to cope promptly with the situation in which the Air/Fuel ratio changes suddenly in response to sudden variations in driving conditions. For example, accelerating after decelerating causes a transition from having a large negative pressure in the intake manifold to having a barely negative pressure in the intake manifold. The large negative intake manifold pressure makes the evaporated gas flow easily, but a barely negative intake manifold pressure reduces the evaporated gas flow. Thus, the flow of evaporated gas is reduced when acceleration occurs and the final Air/Fuel ratio becomes extremely lean. This causes drivability to deteriorate correspondingly and noxious exhaust gas expulsion to increase. Furthermore, when the Air/Fuel ratio becomes excessively lean, the engine may even stop, potentially causing a dangerous situation.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.
The present invention is an improved method and system for controlling fuel for an engine. An embodiment of the invention prevents a lean Air/Fuel ratio and maintains a smoothly running engine when the amount of fuel needs to be changed suddenly, such as the case where the amount of injected fuel is insufficient when compared with the amount of drawn air because the inflow of evaporated gas into the engine is suddenly reduced.
A preferred embodiment of a system of the present invention for controlling fuel for an engine includes: a throttle open-angle detector for detecting a throttle valve open-angle; an oxygen concentration detector for detecting oxygen concentration of exhaust gas; a mass air flow detector for detecting an amount of air drawn into the engine; fuel injectors for injecting fuel to be supplied to the engine; and an electronic control unit for controlling the fuel injectors based on an amount of fuel to be supplied to the engine. The amount of fuel is calculated based on signals received from the detectors. The electronic control unit executes instructions for controlling fuel according to a control logic as described hereinafter.
In another preferred embodiment of the present invention, a method for controlling fuel for an engine includes: determining whether a base amount of fuel is reduced by more than a predetermined amount, the base amount of fuel being reduced according to one or more compensation variables calculated on the basis of an oxygen sensor signal; determining whether a change rate of a throttle valve open-angle is more than a predetermined change rate; initializing the compensation variables when the base amount of fuel is reduced by more than the predetermined amount, and the change rate of the throttle valve open-angle is more than the predetermined change rate; and repeating the calculation of the amount of fuel on the basis of the initialized compensation variables until a predetermined time after the initializing. The initializing of one or more compensation variables may initialize the variables to values that do not affect calculation of the amount of fuel. Preferably, the one or more compensation variables include a feedback gain calculated on the basis of said oxygen sensor signal and a learned reduction value calculated according to said feedback gain. When the base amount of fuel is compensated according to the one or more compensation variables by multiplying the feedback gain and the learned reduction value to the base amount of fuel, the initializing the one or more compensation variables may initialize the feedback gain and the learned reduction value to a value of one (xe2x80x9c1xe2x80x9d).
Preferably, while repeating the calculation of an amount of fuel on the basis of the initialized compensation variables, the method of the present invention determines whether a current change rate of the throttle valve open-angle is reduced by more than a predetermined change rate, and suspends repeating the calculation of the amount of fuel on the basis of the initialized compensation variables when the current change rate of the throttle valve open-angle is less than the predetermined change rate.